The long-term goals of this research project are to elucidate the nature of cellular memory traces, the mechanisms underlying their formation, their duration, and the neurons in which they form within the Drosophila olfactory nervous system. Recent advances in optical imaging of neural activity in specific neurons of the fly's brain have allowed for the visualization of an olfactory memory trace for the first time. Experiments that will extend these observations are proposed. The complete representation of odors by neural activity in the antennal lobe will be elucidated along with the changes in this representation that occur with conditioning. The mechanisms underlying these changes in representation, or memory traces, will be probed using mutants and the expression of functionally inactivating transgenes. The naive and conditioned odorant responses that occur within other neurons of the olfactory nervous system, including the DPM and mushroom body neurons, will be studied using these same optical imaging techniques. The proposed experiments will detect these memory traces, and provide knowledge about their persistence and their specificity to conditioned odors. The mechanisms underlying the formation of DPM and mushroom body neuron memory traces will also be probed using mutants and functionally inactivating transgenes. The hypothesis that dopaminergic neurons convey the unconditioned stimulus to mushroom body neurons will be tested by examining dopaminergic responses to unconditioned and conditioned stimuli. Finally, comparisons will be made between the cellular memory traces that form in the olfactory nervous system using aversive unconditioned stimuli and appetitive unconditioned stimuli with the same odor conditioned stimulus. These experiments will significantly increase our understanding of how memories form and the events that can potentially perturb normal memory formation. This will aid in our understanding of the diseases that affect memory formation.